At around 13:30 one of our servers had a disk problem, and it needs to be rebooted and fixed. This server is hypervisor that runs some of our core services. As we run many redundant and spare servers which fail over to other servers when a problem occurs the customer impact is minimal.
Services restored at around 15:07
One server that was out of action for a while was our Secondary DNS server (secondary-dns.co.uk) - although we would still be serving DNS via primary-dns.co.uk, this may have been noticed by customer's own monitoring systems.